An aircraft gas turbine engine requires a compressor and a turbine. The compressor frequently is in two sections, there being a low pressure compressor and a high pressure compressor. Low weight is important and it is desirable to maintain a good margin from engine surge or stall. Close spacing of the vanes and blades is desirable to minimize the length and weight of the compressor, although enough spacing must be left to tolerate deflection under loads and thermal expansion differences without rubbing.
Uniform clearance between the rotating blades and the casing is desirable since this provides a better surge margin. A structure should be supplied which permits design tuning for thermal inertia of the adjacent parts during transients.
It is also desirable that the vanes be mechanically damped to avoid high stresses with synchronous vibration.
Certain surfaces are wear prone. It is desirable to provide these surfaces in a manner that they may receive surface treatment not only originally, but also during rework for maintenance.
Should there be a need to change the aerodynamics of the compressor, it is desirable that this be possible without changing the case.
Simple fabrication is always desirable since this leads to low cost hardware. The vanes are preferably installed in a manner with tight clearances to minimize vane sloping. The vanes can rotate around their support point if there is excessive clearance, thereby decreasing the actual spacing between the vanes and the blades.
In one prior art system there is a "T" shaped air seal which is a full ring surrounding the location of a compressor blade. This "T" seal carries an abradable surface on the inside edge. Adjacent to "T" shaped air seal, vanes are individually supported on a support member. This support member has a tongue which fits within a groove in the air seal. Assembly of the turbine requires that the vane be radially installed and that thereafter moved axially so that the tongue may then engage within the groove. The groove is not readily accessible for surface treatment. Multiple tolerances are involved in forming this tongue and groove circumferential structure.